SEATTLE (AP) — Washington authorities plan to extradite a man caught in Oregon who’s suspected of killing his grandparents after they picked him up from prison and hosted a welcome home party for him.

King County prosecutors in Seattle expect to file charges against Michael Chadd Boysen, spokesman Dan Donohoe said Wednesday.

Boysen, 26, is accused of killing Robert R. Taylor, 82, and Norma J. Taylor, 80, after they welcomed him to their Renton home after his release from prison Friday.

He was held on a no-bail warrant from the Washington Department of Corrections for violating terms of his release, Donohoe said.

Boysen remains at Legacy Emanuel Medical Center in Portland, Ore., in serious condition, spokeswoman Amber Shoebridge said Wednesday. He had been in critical condition after he was found with self-inflicted cuts Tuesday evening when police stormed an Oregon coast motel room to arrest him.

Investigators don’t know why he went to Lincoln City, Ore., said King County sheriff’s Sgt. Cindi West. They also don’t know what might have motivated the killing of his grandparents.

The King County medical examiner’s office likely will release information Thursday about how the couple died, West said.

Officials believe the Taylors were killed Saturday. Their bodies were found by Boysen’s mother when she went to check on her parents.

Detectives have determined that Boysen checked in under his own name and spent Saturday night at a motel in the south Seattle suburb of Tukwila, not far from his grandparents’ home, West said.

On Monday night, Boysen checked in to the WestShore OceanFront Suites in Lincoln City — again under his own name. Early Tuesday morning, a motel employee alerted police after recognizing his name and face on a TV news show.

King County sheriff’s detectives say Oregon State Police found the Taylors’ missing car Tuesday in a Wal-Mart parking lot in Salem, Ore. West says Boysen paid cash for a used Ford Taurus at a nearby used car lot.

At the Oregon coast motel, Boysen reportedly blocked the door of his room with a refrigerator. Police used a robot to urge him to surrender, and used a water cannon and tear gas before breaking through the door.

Officers found him lying on the floor on his back with apparently serious self-inflicted cuts, Lincoln City police Chief Keith Kilian said.

King County Sheriff John Urquhart called Boysen extremely dangerous because of threats he had made while in prison against his family and law enforcement. Authorities didn’t learn of the threats until after he made the news, suspected of killing in his grandparents.

The Taylors had picked him up from the Washington state prison at Monroe. They drove him to a meeting with a parole officer Friday, helped him get an identity card from the Department of Licensing and held a party for him.

Boysen had just finished serving nine months in prison on a burglary conviction, said Washington state Corrections Department spokesman Chad Lewis. He was previously in prison between 2006 and February 2011 for four robbery convictions. Those convictions were related to an addiction to narcotic painkillers, Lewis said.